Proton and deuteron structure functions in muon scattering at 470 GeV

The proton and deuteron structure functions [Formula presented] and [Formula presented] are measured in inelastic muon scattering with an average beam energy of 470 GeV. The data were taken at Fermilab experiment E665 during 1991 and 1992 using liquid hydrogen and deuterium targets. The [Formula presented] measurements are reported in the range [Formula presented] and [Formula presented] Ge[Formula presented]. These are the first precise measurements of [Formula presented] in the low [Formula presented] and [Formula presented] range of the data. In the high [Formula presented] range of the data where they overlap in [Formula presented] and [Formula presented] with the measurements from NMC, the two measurements are in agreement. The E665 data also overlap in [Formula presented] with the DESY HERA data, and there is a smooth connection in [Formula presented] between the two data sets. At high [Formula presented] the E665 measurements are consistent with QCD-evolved leading twist structure function models. The data are qualitatively described by structure function models incorporating the hadronic nature of the photon at low [Formula presented]. The [Formula presented] and the [Formula presented] dependence of the data measure the transition in the nature of the photon between a pointlike probe at high [Formula presented] and a hadronic object at low [Formula presented].